Microsoft has issued a Surface Pro 2 update to fix glitches introduced by a December firmware release, which reduced battery life and changed how the device went into or out of sleep mode.

After releasing the Dec. 10 firmware update that caused the problems, Microsoft pulled it, but not before some users had downloaded it.

"This weekend we released an update that addresses the unexpected wake and battery drain behavior experienced by a small number of Surface Pro 2 customers who installed the December Windows Update," according to a statement sent by Microsoft's public relations firm, Waggener Edstrom Communications. "This should have no impact on customers who had not received the December update."

Other users reported a variety of wake and sleep issues, saying the devices shut down completely when the cover was closed, rather than going into power-saving sleep mode, or that the machines would not go into sleep mode even when the cover was closed.